Programming exercise participation rate exceeds 100% if instructors or admins participate

[martinmo]

Describe the bug

The participation rate for a programming exercise can be above 100% if users participate who are not part of the corresponding student group of the course (e.g., instructors or admins, probably also tutors and editors – I did not test that).

To Reproduce

1. Create an empty course.
2. Add one student to that course.
3. In that course, create a new programming exercise.
4. Start the exercise as the student.
5. Start the exercise as the instructor.
6. In the course management, navigate to the exercise and see that its participation rate is 200%.

Expected behavior

The participation rate should not exceed 100%. Participations by users not part of the course's students group should not be counted.

Screenshots

If the student group is empty and the instructor participates:

What browsers are you seeing the problem on?

Firefox

Additional context

No response

Relevant log output

No response